Because SCLs are made of materials having a high water content and flexibility, they can provide a more comfortable fit for wearers, and can be worn for a long period of time compared with hard contact lenses. Therefore they have been widely used. With the increase in the number of SCL users, recently, ophthalmic compositions for SCL (including eye drops and eye washes that can be used when wearing SCLs, wetting and rewetting drops for SCL, SCL care solutions, and the like) containing various components have also been proposed. Of these compositions, ophthalmic compositions for SCL comprising a terpenoid such as menthol or camphor have attracted attention, because they are expected to have an effect of alleviating stimulation, thus reducing discomfort, or providing a cool and refreshing feeling.
However, SCLs have a specific problem in that terpenoids adsorb to the SCLs. When terpenoids adsorb to and deposit on an SCL, the SCL may be deformed, and this sometimes causes a decrease in wettability, or an adverse affect on feeling while wearing, such as a foreign-body feeling or discomfort. For this reason, when a terpenoid is added to ophthalmic compositions for SCL (including eye drops and eye washes that can be used when wearing SCLs, wetting and rewetting drops for SCL, SCL care solutions, and the like), it is essential to suppress the adsorption of the terpenoid.
It has hitherto been reported that the addition of a surfactant is effective for reducing the adsorption of a terpenoid to an SCL. When a surfactant is added, however, defects such as coloring of the resulting ophthalmic composition for SCL can be caused depending on the type or proportion of the surfactant; there can also be disadvantages such as difficulty in handling during production because of bubbling. Under such circumstances, the development of a novel technique for suppressing the adsorption of a terpenoid to an SCL has been demanded.
On the other hand, alginic acid forms gel (becoming more viscous) by being partially cross-linked with a divalent or higher valent cation such as a Ca2+ ion, and it is already recognized that the alginic acid is an available component in the ophthalmic field (see, for example, Patent Document 1). Furthermore, it has also been found that when an eye drop comprising alginic acid is applied to an eye, Ca2+ ions existing on an ocular mucosa are contacted with the alginic acid to make the eye drop gel (become more viscous) on the ocular mucosa, and therefore the alginic acid is useful for improving the retention of the eye drop on the ocular mucosa and maintaining effects produced by active ingredients. However, it has not been reported that 0.005% by weight or more of a terpenoid is used together with alginic acid in an ophthalmic composition for an SCL. Additionally, it is not entirely understood what effect the alginic acid exerts on the adsorption of the terpenoid within such a concentration range to the SCL.    Patent Document 1—Japanese Patent Application Laid-Open Publication No. 2002-332248